1. Field of the Invention
This invention relates to a recording apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus and specifically a copying apparatus, a printer or a facsimile apparatus, and more particularly to a recording apparatus provided with a mechanism for applying parting liquid as an offset preventing agent to a fixing rotatable member when toner in the form of dust, powder or capsule is fixed on a recording medium.
2. Description of the Prior Art
The recording apparatus to which the present invention pertains generally uses a fixing device in which a recording medium is passed between a pair of rollers as a pair of fixing rotatable members and a dust toner image is fixed on the recording medium by applying a pressure or heat and pressure to between the pair of rollers.
Such fixing device has many advantages as compared with conventional devices while, on the other hand, it has a fault. The fault is that the dust toner image directly contacts the fixing rollers and therefore the toner to be fixed on the recording medium such as low temperature offset or high temperature offset may adhere to the surfaces of the rollers. When the toner adheres to the surfaces of the rollers, it may affect the image on the next recording medium passing between the rollers and the toner may be fixed on unexpected parts of the recording medium or may stain the recording medium. To avoid occurrence of such problem, it is generally practised to apply a parting agent such as silicon oil to the surfaces of the rollers to thereby prevent offset.
The toner offset preventing method using the application of the parting agent may cause the following problem to arise depending on the material of the recording medium.
The parting agent applied onto the rollers, conversely to toner, adheres to the recording medium to a certain degree as the recording medium passes between the rollers, and where the recording medium is, for example, paper, the parting agent having adhered to the paper is absorbed into the paper and there arises no problem, but where the recording medium does not have such an absorbing capability, there arises a problem that the parting agent having adhered to the surface of the recording medium intactly stagnates on that surface. As a recording medium of such a material, mention may typically be made of a resin material such as trapen film used, for example, for OHP (overhead projector). Such stagnation of the parting agent on the surface of the recording medium makes the surface of the recording medium discharged from the fixing station wet with the parting agent and makes the sense of touch of the recording medium very bad. Particularly, in a color image copying apparatus or the like in which, for smoothing the mixing of three primary color toners during fixation, toners of low fusing point are used to provide better fluidity during heating for fixation, a relatively great amount of silicon oil is applied to the fixing rollers and therefore much silicon oil adheres to the recording medium and thus, the sense of dipleasure thereof is very remarkable. This problem is not limited to the sense of touch, but if the recording medium is kept in contact with other paper or the like for a long time, the parting agent may permeate into the paper and stain the paper and further, if recording mediums wet with the parting agent are superimpose one upon the other, the recording mediums may adhere to each other due to the parting agent and cannot be handled properly, and this may lead to cumbersomeness of the arrangement or treatment of the recording mediums, and may further lead to a problem that writing of characters or the like onto the recording medium by magic ink or a felt pen becomes impossible because the parting agent on the surface of the recording medium rejects such ink.
Particularly, if much of this parting agent adheres to the resin film for OHP, it may cause the parting agent to interfere with the transmitted light and may result in unsharp images.
Against such a problem, it has heretofore been practised to reduce the amount of parting agent applied to the fixing rollers, but a sufficient effect has not been obtained and especially in the case of resin film, this problem has not been solved at all.
The present invention provides a solution to such problem and achieves a novel and important effect.